We have encountered many tunnels during treasure hunting and mostly were closed tunnels bearing codes and signs near a slab of stone and perfectly etched. Sometimes it is pointed by a large nail that was put on an old tree or a large one. Inside a tunnel may lead to an empty room but in some stories that I have heard, there are large volumes of treasure were put and at the middle of the room there is golden Buddha surrounding other treasures and gold bars around. Other tunnels may also have booby traps which may be triggered when stepped on as some are bombs or landmines that are still very active due to they have put some oil/grease to prevent corrosion over time.
Above picture was taken in Nueva Ecija, this is just one of the open tunnels that we have found on the mountain. Near this tunnel are closed tunnels which was dug by fellow treasure hunters and found some old relics during the war including old curtains that was used by the Japanese officials as their door inside the tunnels. Water is near and it is probably their water source during the war. According to the Old locals whom have been residing during the war told has that it was the Japanese hideout until their surrender and many still unknown tunnels in the mountain were still there until now.
Letter signs that were used to indicate a nearby tunnel etched in a stone based from the code that I have borrowed from fellow treasure hunters. And below are some of the symbol that the Japanese used as a code for a tunnel containing deposits.